In recent years, in the field of flexographic printing, a CTP Technique, known as a digital image-forming technique, has been widely used as a general technique. The CTP technique is a method in which information processed on a computer is directly outputted onto a printing plate so that a concave/convex pattern to form a relief is obtained. This technique eliminates the necessity of negative film producing steps, thereby making it possible to reduce costs and time required for forming the negative film.
As to a CTP photosensitive flexographic printing original plate, there has been proposed a water-developable flexographic printing original plate having such a constitution that a protective layer (barrier layer) is formed on a photosensitive resin layer and a heat-sensitive mask layer is further formed thereon (Patent Document 1). Although the Patent Document 1 can provide a photosensitive flexographic printing original plate having an excellent laser ablation property, it results in a printing blur which is nothing wrong in a negative system. To begin with, the ablation layer formed for CTP is easily deformed as compared with a negative film. Therefore, there is a disadvantage that the shape of the relief top area is easily deformed. Accordingly, in the printing, uneven transfer of ink (printing blur) caused by bulging of the edge as such has been apt to be generated.
In addition, in the photosensitive resin composition of Patent Document 1 for the CTP photosensitive flexographic printing original plate, there are disadvantages that mechanical strength is insufficient and printing durability upon printing is insufficient and there has been a demand for improvements thereof.
As such, the conventional CTP flexographic printing original plate using a water-developable photosensitive resin composition does not satisfy the requirements for solving all of laser ablation property, water developing ability, printing durability and a printing blur as a result of changes in relief top shape.